The present invention relates to a tensioning device for a power transmission chain system. More particularly, the present invention relates to a tensioning device having an adjustable snubber for eliminating the decrease in chain tension on the tight side of a chain system caused by manufacturing tolerances in the chain components.
Power transmission chain systems for automotive applications typically include at least two sprockets and an endless chain wrapped around the sprockets. As the driving sprocket transmits power to the chain, which then transmits power to the driven sprocket, a tight side and a slack side of the chain is formed in the span or length of chain between the sprockets.
In a chain drive system, a tensioning device is generally provided for taking-up or compensating for looseness on the slack side of the chain. The slack take-up device, or tensioner, is generally in one of two categories: a hydraulic tensioner made up of a hydraulic cylinder piston assembly which carries on its moveable member a tensioner arm or pad designed to contact the chain and resist inward movement of the chain by spring and hydraulic pressure; a mechanical tensioner which, on the other hand, exploits the action of a helical or leaf spring that causes the tensioner arm or chain guide to move outward and eliminate slack in the chain.
The tensioner device takes up both the slack due to the wear of the chain and the sprockets, and the slack or the tolerances due to any initial errors in assembly. As a result, however, the moveable member of the tensioner, in order to have a desired effect, must have a considerable range of movement. Another result is that sometimes an initial adjustment, or a take-up of initial assembly tolerances, when they are significant, jeopardizes the possibility of compensating wear during the later stages of the life of the chain, in that the range of movement of the tensioner arm is largely or completely utilized in initial adjustment for tolerances.
Furthermore, the known systems generally have a fixed chain guide or snubber on the tight strand of the chain. In view of the limited slack on the tight strand of the chain, the snubber or chain guide typically does not expand outward to take up the slack in the chain. Thus, the snubber does not provide an outward movement to take up the slack due to manufacturing tolerances.
There is therefore the need in the chain art to obtain a satisfactory take-up of slack, whether due to assembly or manufacturing tolerances inherent in the system, or due to the wear between the parts that occurs with time.
The device of the present invention is directed to that problem.